Oxidation of olefinic compounds



y 7, 1953 c. E. SCHWEITZER 2,644,837

OXIDATION OF OLEFINIC COMPOUNDS Filed April 27, 1951 RECOVERY 5 RECYCLED HYDROCARBO/V HYDROGARBON noon/01v PLUS ernooucrs 1 1 uns: -P-

PRODUCT HYDROCARBON u STRl-PER r0005 :5, PlIfiF/[D LAYER l2 nooucr mooucr 4 l6 RECYCLED WA TER PURGE PLUS BY-PRODUCTS H 20 STRIPPER LAYER v 9 PRODUCT A A r f FEED AIR

WATER ADDITION INVENTOR:

CA RL E. SCHWEITZER A 1mm 2/ 04 0. M

' ATTORNEY.

Patented July 7, 1 953 OXIDATION OF OLEFINIC COMPOUNDS Carl E. Schweitzer, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application April 27, 1951, Serial No. 223,224

11 Claims.

This invention relates to a process for oxidizing organic compounds containing an olefinic linkage to obtain the corresponding dihydroxy derivative. In a particular embodiment it relates to a process for oxidizing isobutylene to isobutylene glycol.

Various processes have been proposed for converting compounds which contain an olefinic linkage into the corresponding dihydroxy derivative. For the most part, these processes have been based upon the use of chemical oxidizing agents, including the peroxides such as hydrogen peroxide. These prior art processes have not been entirely satisfactory for commercial operations, either because the starting materials were expensive or else because the desired products were not obtained in sufiicient yield or in a sufficiently high degree of purity.

It is an object of this invention to provide a process for oxidizing organic compounds which contain the olefinic linkage Another object of the invention is to rovide a process for converting compounds which contain an olefinic linkage into the dihydroxy derivative thereof. A particular object of the invention is to provide a process for oxidizing isobutylene to isobutylene glycol in high yield. Other objects of the invention will appear hereinafter.

In accordance with this invention there is provided a process which comprises subjecting an organic carbon compound containing from 2 to 6 carbon atoms and containing a single olefinic linkage to oxidation at superatmospheric pressure and at a temperature in excess of 100C. in the presence Of ingredients comprising (a) an oxygen-containing gas, (2)) a medium comprising water and an inert liquid hydrocarbon, and (c) a recycled by-product produced in a previous oxidation of the said organic carbon compound with an oxygen-containing gas, and separating a polyhydroxy compound from the resulting reaction medium.

In accordance with a preferred embodiment of the invention, isobutylene is subjected to oxidation with air in a continuous process and in the presence of a benzene/water medium, and a portion of the by-products remaining in the henzene/water medium after removal of isobutylene glycol is continuously recycled to the oxidation zone.

According to another feature of the invention, there is provided a process which comprises subjecting an organic compound containing from 2 to 6 carbon atoms and containing a single olefinic linkage to oxidation at superatmospheric pressure and at a temperature in excess of 100 C. in the presence of an oxygen-containing gas, a solvent comprising water and an inert liquid hydrocarbon, and a soluble catalyst of the group consisting of the soluble manganese, iron, chromium, nickel, copper, molybdenum, zinc, tin, vanadium, silver, and lead compounds.

Compounds which can be oxidized in accordance with this invention include not only the olefinic hydrocarbons, but also the compounds which contain an oxygenated grouping in addition to the olefinic linkage. All of the suitable compounds are characterized by the presence of the linkage. Included among the suitable olefinic compounds are ethylene, propylene, butylene, isobutylene, the pentenes and the hexenes; allyl alcohol, methallyl alcohol, acrolein, methacrolein, methyl vinyl ketone, methyl isopropenyl ketone, methyl vinyl ether, vinyl acetate; acrylic acid, methacrylic acid, crotonic acid and the lower alkyl esters thereof; and the like.

The compounds which are produced are derivatives 0f the original olefinic compounds in which a hydroxy group is attached to each of the carbon atoms which formed the olefinic linkage. For example, in the case of ethylene, the desired product would be ethylene glycol; in the case of isobutylene, the desired product would be isobutylene glycol, i. e., 2-methyl-l,2-propanediol; and in the case of methallyl alcohol, the product would be 2-methyl-1,2,3-propanetriol.

The oxidizing agent employed is molecular oxygen, either as such or diluted with other gases, as in the case of air. Since excellent results are obtained with air, it constitutes the preferred oxidizing agent because, of course, of its ready availability and almost negligible cost. If desired, however, pure oxygen, or oxygen, or air enriched with oxygen, or the like may be employed.

Suitable solvents include mixtures of water with inert liquid hydrocarbons such as benzene, toluene, xylene, cyclohexane, parafiinic compounds such as the hexanes, the octanes, etc. The prime requisite of the hydrocarbon is that it be substantially inert under the prevailing oxidation conditions. Benzene/Water media constitute much the most satisfactory solvents. The water and inert liquid hydrocarbon may be employed in ratios of from 1:30 to 20:1, with ratios 3 of from 1:2 to 1:1 being preferred. These inert liquid hydrocarbons are for the most part immiscible with the water.

A very important feature of the present invention is the recycling to the oxidation zone of at least a portion of the by-products resulting from a previous oxidation of the same organic compound. For reasons which are not fully understood, the recycling of such by-products greatly increases the yield obtained in the oxidation. At the completion of a given run, some of the desired polyhydroxy compound and some of the by-products will be dissolved in each of the water and hydrocarbon layers. After removal of the polyhydroxy compound from the solvent by methods described hereinafter, the by-products remaining in either the water or the hydrocarbon phase solvent, or both, are recycled to the oxidation zone. Preferably, all of the by-products remaining both in the water and hydrocarbon layers are recycled to the oxidation zone in a continuous process, with suitable proportions of the by-products being purged in order to prevent too great an accumulation thereof.

As will be shown in the examples, this recycling becomes progressively more advantageous during the first several stages. Oxidation in the absence of either a catalyst or recycled by-products is very unsatisfactory. When oxidation is initiated, for instance, with a catalyst, and the by-products from this oxidation are employed in a second oxidation, fair yields are obtained in the second oxidation even in the absence of an added metalcompound catalyst. When the by-products from this second oxidation are passed to a third oxidation zone, even better yields are obtained, and when this process is repeated in a fourth oxidation zone, excellent results are obtained. In view of this phenomenon, it will be appreciated that continuous operation of this process results in striking advantages, on a commercial scale, as compared to batch operation.

As pointed out above, the soluble salts of manganese, iron, chromium, etc. are useful in promoting the oxidation of the olefinic compounds to the corresponding glycols. Catalysts include the alkali chromates, dichromates, permanganates, ferricyanides, stannates, zincates, vanadates, plumbates, and the like. In the absence of any recycled by-products, the use of a catalyst to initiate the oxidation is essential for practical commercial operations, and catalysts may also be employed advantageously in conjunction with the recycled by-products. One of the great advantages of the present invention, however, is that these catalysts may be dispensed with, once the process has been set up and the accumulated by-products from several successive oxidations are available.

Another advantage of recycling by-products from the oxidation is that it makes possible the use of temperatures which are significantly lower than would otherwise be feasible for commercial air oxidations of this type. For example, when operating in the absence of any recycled by-product, temperatures of from 160 to 170 C. are necessary in order to obtain oxidation of isobutylene, whereas temperatures of only 135 to 140 C. are sufficient when operating under the optimum recycle conditions. In general, temperatures in excess of 100 C. are employed. Temperatures within the range of from 100 to 200 C. are preferred, and when operating in the presence of recycled by-products, temperatures of from 100 to 160 C. are particularly preferred.

Pressures in excess of 200 pounds per square inch are generally employed, with pressures of from 200 to 2000 pounds per square inch being preferred. The oxidation is preferably carried out at pHs close to 7, but relatively more acidic or basic conditions can also be employed to good advantage.

The product can be recovered from the solvent by a number of different techniques. It is generally preferred to pass the water layer and the hydrocarbon layer to strippers in which the solvent and the low-boiling by-products are removed by distillation. Part or all of the solvents or byproducts may be recycled to the oxidation zone. The crude polyhydroxy compound may then be purified, by suitable techniques, to any desired extent. This purification may involve, for instance, chemical separations, solvent extraction, selective absorption, simple fractionation, steam distillation, azeotropic distillation, extractive distillation, or the like.

The optimum purification procedure will, of course, depend upon the particular polyhydroxy compound which is being purified and the particular impurities which it is desired to remove therefrom. Acid impurities are conveniently removed by neutralization with a suitable base, followed by filtration. Some of the impurities may be combined in the form of esters of the polyhydroxy compound. These esters may be hydrolyzed by known methods and the polyhydroxy compound recovered therefrom. Steam distillation is advantageously employed to remove water-immiscible impurities.

In the case of isobutylene, the main by-product is acetone, while tertiary butanol, isobutylene oxide, methanol, isoamyl alcohol, isopropyl alcohol, allyl alcohol, formaldehyde and acetic acid have all been identified in the crude oxidation mixture, and small amounts of peroxides may also be present. After removal of the low-boiling by-products in the strippers, a useful procedure for purifying the crude isobutylene glycol involves neutralization with sodium hydroxide or with lime followed by filtration to remove acids present. Acid-free glycol is then ester-exchanged with methanol using an acid catalyst in order to liberate any glycol combined as esters. Finally the partly refined glycol is steam distilled to remove water-immiscible impurities and then redistilled to produce substantially pure isobutylene glycol. The crude isobutylene glycol from the water stripper may be combined with that from the hydrocarbon stripper, and the whole subjected to a combined purification treatment. Alternately, the two crude isobutylene compositions may be purified separately if desired.

A preferred method for carrying out the process of the present invention is shown diagrammatically in the accompanying drawing, which represents the air oxidation of an olefin such as isobutylene to produce the corresponding glycol. Referring now to the drawing, numeral l represents an oxidation chamber into which olefin feed is continuously introduced via inlet pipe 2 and air is continuously introduced via inlet pipe 3. The oxidation chamber l contains a mixed water/ hydrocarbon reaction medium. Additional water may be introduced as needed via inlet pipe 4 and additional hydrocarbon may be introduced as needed via pipe [1. The oxidation reaction takes place in oxidation zone I at a temperature of about to C. and'at a pressure of 200 to 2000 pounds per square inch. Gases which collect at the top of the oxidation zone I are removed continuously to the olefin recovery unit 5 in which any unreacted olefin is recovered and returned via lines 6 and 2 to the oxidation chamber. Other gases such as nitrogen, carbon monoxide and carbon dioxide are removed from the system via vent l. is continuously removed from the oxidation zone I via line 8 to stripper 9. Water and low-boiling by-products are removed by distillation and returned to the oxidation zone I via line It. A portion of these by-products may be purged from the system by removal from line H]. A portion of the hydrocarbon layer is continuously removed from the oxidation zone 1 via line ll to stripper I 2. are removed by distillation and recycled to the system via line l3, with a suitable purge being taken. Crude glycol from stripper 9 passes via line 14 to be combined in line I5 with crude glycol removed from stripper l2. The combined crude glycol streams pass to the glycol refining unit l6 where the crude glycol is subjected successively to acid neutralization and filtration, ester exchange, steam distillation, and final distillation, to produce purified glycol.

The invention will be illustrated further by the following examples:

Example 1.-This example represents the third oxidation carried out in a recycle study. In other words, portions of the by-products contained in the benzene and water had already been through two previous oxidations. A mixture composed of 100 parts of water and 200 parts of benzene, each containing by-products recovered from the previous oxidation stage, 1 part of potassium dichromate and 251.4 parts of isobutylene was charged into a tantalum-lined bubble-type oxidizer. The temperature was raised to 135 C. and air at 900 pounds per square inch gauge was bubbled up through the reactants for about two hours. Oxygen in the oil gas dropped from about 21% to 0.4% and small amounts of carbon oxides were evolved. The amount of isobutylene consumed was 25.4 parts. The benzene and water layers of the reaction mixture were distilled separately giving a total of 32.5 parts of crude glycol (boiling point 50 to 62 C./2 mm). Analysis of this crude glycol composition showed that it contained 19.4 parts of free isobutylene glycol and 4.1 parts of isobutylene glycol in a combined form, making a total of 23.5 parts of isobutylene glycol, which represents a yield of 59 Example 2.-This example shows the pronounced effect on the glycol yield and the oxidation temperature which results from the recycling of the by-products. Three successive runs were made in which isobutylene was oxidized with air in the presence of a benzene/water medium containing about 2 parts of benzene per part of water. Pressures of about 800 to 900 pounds per square inch were employed and small amounts of potassium dichromate catalyst were present. In the initial run, made with fresh benzene and water which contained no recycled by-product, a temperature of 160 to 170 C. was required in order to obtain good oxygen clean-up, and the yield was less than 30%. In the second run, using benzene and water which contained byproducts produced in the first run, a yield of 50% was obtained. In the third run, using benzene and water which contained by-products produced in the second run, the oxidation temperature could be reduced from 160-1'70 C. to 135-140 C. without sacrificing good oxygen clean-up, and a yield of 58 was obtained.

A portion of the water layer Hydrocarbon and low-boiling by-products Ezvample 3.-This example shows a method for refining crude isobutylene glycol separated from the water layer removed from the oxidation zone. The crude isobutylene glycol (156.2 parts), which contained about of pure isobutylene glycol, was mixed withan equal weight of methanol. Sodium methoxide was added until a pH of 8-9 was obtained and the mixture was refluxed to remove methyl acetate. Distillation of the remaining mixture gave 126 parts of substantially pure isobutylene glycol (boiling point 54-56" C./2 mm.).

Emample 4.This example shows the purification of crude isobutylene glycol derived from the benzene layer removed from the oxidation zone. The crude isobutylene (183 parts), containing about 56% free glycol and 14% combined glycol, was mixed with an equal weight of methanol and made alkaline with sodium methoxide. Refluxing the mixture resulted in ester exchange which produced a small amount of methyl acetate. Methanol was removed and the glycol was distilled. This product was subjected to steamdistillation which removed about 2% as a waterimmiscible layer. Distillation of the product then gave a water-white, completely watermiscible liquid which analyzed as isobutylene glycol.

Attempts to carry out the oxidation in either water or benzene alone met with poor success as compared to the excellent results which were obtained when using two immiscible liquids together.

When working with compounds other than isobutylene, conditions of temperature and pressure varying slightly from those shown in the foregoing examples were required in order to obtain optimum yields. Excellent results are obtainable, however, when the principles-illustrated by these examples are followed, but other compounds such as' propylene, allyl alcohol, methallyl alcohol, methacrylic acid, methyl methacrylate, etc., are substituted for the isobutylene.

Good mechanical agitation may be helpful in obtaining high yields in .this oxidation process, but agitation is not believed to be critical. In fact, one of the surprising features of the present invention is the excellent degree of oxygen clean-up which was obtained in some of the experiments even though there was little agitation and very little mixing of the water and hydrocarbon layers, even at the interface. Hence, the process may be carried out using only the agitation which results from the air passing through the water-hydrocarbon medium or, if desired, mechanical agitation mayalso be employed.

The process may be carried out in equipment constructed of any of a number of materials generally employed in the industry. Steel and in particular stainless steel, nickel, tantalum, titanium, stoneware, and the like may be employed satisfactorily.

Since many modifications in the process as described can be made by those skilled in the art without departing from the spirit and scope of the invention, it is not intended that the invention should be restricted other than by the following claims.

I claim:

1. A process which comprises subjecting an organic carbon compound containing from 2 to 6 carbon atoms and containing a single olefinic linkage to oxidation at superatmospheric pressure and at a temperature in excess of C. in the presence of ingredients comprising (a) an oxygen-containing gas, (b) a medium comprising water and an inert liquid hydrocarbon, and (c) a recycled by-product produced in a previous oxidation of the said organic carbon compound with an oxygen-containing gas, and separating a polyhydroxy compound from the resulting re action medium.

2. A process according-to claim 1 in which the organic carbon compound is isobutylene.

3. A process according to claim 1 in which the organic carbon compound is allyl alcohol.

4. A process according t claim 1 in which the carbon compound is methyl methacrylate.

5. A process according to claim 1 in which'the oxygen-containing gas is air.

6. A process according to claim 1 in which the inert liquid hydrocarbon is-benzene;

7'. A process according toclaim 1 which is operated in a continuous manner and in which a byproduct produced in the oxidation zone is continuously recycled, with purging, to said zone.

8. A process according to claim 1 in which the medium comprises water and benzene and in which said water and benzene, together with lowboiling by-products, are separated from the crude polyhydroxy compound and continuously recycled, with purging, tothe oxidation zone.

9. A continuous process which comprises subjecting isobutylene'to oxidation at a pressure of from 200 to 2000 pounds per square inch and at a temperature of from 100 to 160 C. in the presence of air, a water/benzene medium and byproducts produced in a. previous oxidation of isobutylene under similar conditionswhich are continuously recycled to the oxidation zone, and sep- 3 organic carbon compound containing from 2 to 6 carbon atoms and containing a single olefinic linkage to oxidation at superatmospheric pressure and at a temperature in excess of C. in the presence of ingredients comprising (a) an oxygen-containing gas, (b) a medium comprising water and an inert liquid hydrocarbon, and (c) a soluble catalyst of the group of soluble manganese, iron, chromium, nickel, copper, molybdenum, zinc, tin, vanadium, silver and lead compounds, and separating a polyhydroxy compound from the resulting reaction medium.

11. A process which comprises subjecting an organic carbon compound containing from 2 to 6 carbon atoms and containing a single olefinic linkage to oxidation at a pressure in excess 01' 200 pounds per square inch and at a temperature in excess of 100 C. in the presence of ingredients comprising (a) an oxygen-containing gas, (b) a medium comprising water and an inert liquid hydrocarbon, (c) a recycled by-product produced in a previous oxidation of the said organic carbon compound with an oxygen-containing gas, and (d) a soluble catalyst of the group consisting of soluble manganese, iron, chromium, nickel, copper, molybdenum, zinc, tin, vanadium, silver and lead compounds, and separating a polyhydroxy compound from the resulting reaction medium;

CARL E. SCHWEITZER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,071,395 Dreyfus Feb. 23, 1937 2,316,604 Loder et. a1 Apr. 13, 1943 2,500,599 Bergsteinsson et al. Mar. 14, 1950 

1. A PROCESS WHICH COMPRISES SUBJECTING AN ORGANIC CARBON COMPOUND CONTAINING FROM 2 TO 6 CARBON ATOMS AND CONTAINING A SINGLE OLEFINIC LINKAGE TO OXIDATION AT SUPERATMOSPHERIC PRESSURE AND AT A TEMPERATURE IN EXCESS OF 100* C. IN THE PRESENCE OF INGREDIENTS COMPRISING (A) AN OXYGEN-CONTAINING GAS, (B) A MEDIUM COMPRISING WATER AND AN INERT LIQUID HYDROCARBON, AND (C) A RECYCLED BY-PRODUCT PRODUCED IN A PREVIOUS OXIDATION OF THE SAID ORGANIC CARBON COMPOUND WITH AN OXYGEN-CONTAINING GAS, AND SEPARATING A 